Incorporation of rare-earth atoms into a semiconductor host has received much attention recently due to the potential applications of rare-earth doped materials as efficient optical amplifiers and light-emitters. The outer 5s and 5p shells shield the inner 4f electrons from the surrounding environment, allowing the energy levels of the 4f shell to remain relatively unperturbed when placed into a solid host. By choosing the appropriate rare-earth element, it is possible to create very sharp, temperature-stable light emission based upon intra-4f transitions. A majority of the research done for rare-earth doping has been devoted to the element Er, since one of its 4f transitions produces emission at wavelength (1.54 μm) that corresponds to a minimum loss in modern silica fibers for optical communications. Much of the early work for Er doped III-V semiconductors focused primarily on the known compounds of GaAs, GaP, InP, and Si.4-6 Ennen et al. successfully incorporated Er into these semiconductors by ion-implantation, but the reported quantum efficiency was not of the order acceptable for commercial applications.5 Favennec et al, later showed that the emission efficiency of the intra-4f transitions depends strongly upon the bandgap of the host semiconductor.6 By using ion implantation to incorporate Er into semiconductors with a large diversity of bandgap energies, it was shown that a subsequent thermal quenching of the rare-earth emission occurs for the semiconductors with smaller bandgaps. It has also been suggested that the neighboring environment created by more ionic host semiconductors increases the intra-4f Er3+ transitions.1,7 In light of these properties, GaN is an optimum host for Er since it has a bandgap of 3.4 eV, and an electronegativity difference of −1.2.
Much work has been dedicated to the incorporation of Er into GaN by methods such as ion-implantation, hydride vapor phase epitaxy (HVPE), metal organic molecular beam epitaxy (MOMBE), and molecular beam epitaxy (MBE). There are reports of successful Er incorporation, leading to devices, such as light emitting diodes (LEDs), that produce wavelengths ranging from the visible to infrared. But all such devices still suffer either from strong emission lines in the visible region and/or from a low quantum efficiency at the IR wavelengths, severely limiting their prospects for practical device applications in telecommunication systems.